1. Field of the Invention
The present invention relates to an airbag which is mountable on a vehicle for catching a vehicle occupant such as a driver and a front-seat passenger in the event of an oblique collision or the like.
2. Description of Related Art
JP 2015-116912 A, by way of example, discloses a known airbag, which is an airbag for a driver's seat. The airbag is internally provided with a tether as a countermeasure against a small overlap crash. The tether is arranged along a width direction of a vehicle inside the airbag, and helps the airbag to catch the head, including the face, of the driver who moves in an oblique direction without turning the head in the event of a small overlap crash.
Although the airbag of the above-mentioned reference is prevented from bulging in a width direction of the vehicle at deployment because of the tether, it cannot avoid protruding towards a direction orthogonal to the width direction of the vehicle, i.e., rearward or towards the driver, in an initial phase of airbag deployment. That is, the above airbag has a room for improvement in deployment behavior in the initial phase of deployment.
JP 2005-247272 A discloses another known airbag for a driver's seat which is partitioned into more than one chambers each of which is inflatable with a suitable internal pressure. More specifically, the airbag includes a first chamber which is disposed at the center of the airbag and a second chamber which has such an annular shape as to encircle the first chamber and is inflatable with a lower internal pressure than the first chamber. Each of the first chamber and second chamber has its own circumferential wall, and therefore, the tubular regions of the circumferential walls of the first chamber and second chamber at the border of the first and second chambers are disposed in such a manner as to connect a driver-side wall of the airbag deployable towards the driver and a vehicle-side wall of the airbag deployable towards the vehicle body structure. In other words, the tubular regions of the circumferential walls of the first and second chambers serve as a tether and help prevent the central region of the driver-side wall from protruding too much rearward and towards the driver. However, with the lower internal pressure than the first chamber, the second chamber is easily deformable and thus is not suitable for catching the driver (vehicle occupant) without turning him in the event of an oblique crash.